2.3.2. Feign

Feign介绍

Feign是一个声明式的web service客户端，它使得编写web service客户端更为容易。创建接口，为接口添加注解，即可使用Feign。Feign可以使用Feign注解或者JAX-RS注解，还支持热插拔的编码器和解码器。Spring Cloud为Feign添加了Spring MVC的注解支持，并整合了Ribbon和Eureka来为使用Feign时提供负载均衡。

译自：http://projects.spring.io/spring-cloud/docs/1.0.3/spring-cloud.html#spring-cloud-feign

Feign示例

创建一个Maven项目，并在pom.xml添加如下内容：

  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  3.   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  4.   <modelVersion>4.0.0</modelVersion>
  6.   <artifactId>microservice-consumer-movie-feign</artifactId>
  7.   <packaging>jar</packaging>
  9.   <parent>
  10.     <groupId>com.itmuch.cloud</groupId>
  11.     <artifactId>spring-cloud-microservice-study</artifactId>
  12.     <version>0.0.1-SNAPSHOT</version>
  13.   </parent>
  15.   <dependencies>
  16.     <dependency>
  17.       <groupId>org.springframework.cloud</groupId>
  18.       <artifactId>spring-cloud-starter-eureka</artifactId>
  19.     </dependency>
  21.     <dependency>
  22.       <groupId>org.springframework.cloud</groupId>
  23.       <artifactId>spring-cloud-starter-feign</artifactId>
  24.     </dependency>
  26.     <dependency>
  27.       <groupId>org.springframework.boot</groupId>
  28.       <artifactId>spring-boot-starter-actuator</artifactId>
  29.     </dependency>
  30.   </dependencies>
  31. </project>

启动类：MovieFeignApplication.java

  1. /**
  2.  * 使用@EnableFeignClients开启Feign
  3.  * @author eacdy
  4.  */
  5. @SpringBootApplication
  6. @EnableFeignClients
  7. @EnableDiscoveryClient
  8. public class MovieFeignApplication {
  9.   public static void main(String[] args) {
  10.     SpringApplication.run(MovieFeignApplication.class, args);
  11.   }
  12. }

实体类：User.java

  1. public class User {
  2.   private Long id;
  3.   private String username;
  4.   private Integer age;
  5.   ...
  6.   // getters and setters
  7. }

Feign测试类：UserFeignClient.java。

  1. /**
  2.  * 使用@FeignClient("microservice-provider-user")注解绑定microservice-provider-user服务，还可以使用url参数指定一个URL。
  3.  * @author eacdy
  4.  */
  5. @FeignClient(name = "microservice-provider-user")
  6. public interface UserFeignClient {
  7.   @RequestMapping("/{id}")
  8.   public User findByIdFeign(@RequestParam("id") Long id);
  9. }

Feign的测试类：FeignController.java

  1. @RestController
  2. public class FeignController {
  3.   @Autowired
  4.   private UserFeignClient userFeignClient;
  6.   @GetMapping("feign/{id}")
  7.   public User findByIdFeign(@PathVariable Long id) {
  8.     User user = this.userFeignClient.findByIdFeign(id);
  9.     return user;
  10.   }
  11. }

application.yml

  1. server:
  2.   port: 8020
  3. spring:
  4.   application:
  5.     name: microservice-consumer-movie-feign
  6. eureka:
  7.   client:
  8.     serviceUrl:
  9.       defaultZone: http://discovery:8761/eureka/
  10.   instance:
  11.     preferIpAddress: true
  12. ribbon:
  13.   eureka:
  14.     enabled: true         # 默认为true。如果设置为false，Ribbon将不会从Eureka中获得服务列表，而是使用静态配置的服务列表。静态服务列表可使用：<client>.ribbon.listOfServers来指定。参考：http://projects.spring.io/spring-cloud/docs/1.0.3/spring-cloud.html#spring-cloud-ribbon-without-eureka
  16. ### 参考：https://spring.io/guides/gs/client-side-load-balancing/

同样的，启动该应用，多次访问http://localhost:8020/feign/1，我们会发现和Ribbon示例一样实现了负载均衡。

代码地址（任选其一）：

Feign代码地址：

http://git.oschina.net/itmuch/spring-cloud-study/tree/master/microservice-consumer-movie-feign
https://github.com/eacdy/spring-cloud-study/tree/master/microservice-consumer-movie-feign